Recently, lithium secondary batteries that are chargeable/dischargeable and lightweight and have high energy and output densities are being widely used as energy sources for wireless mobile devices. Also, lithium secondary batteries have attracted considerable attention as power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), and electric vehicles (EVs), which have been developed to solve limitations, such as air pollution and green-house gases, caused by existing internal-combustion engine vehicles that use fossil fuels, such as gasoline and diesel vehicles.
In such a lithium secondary battery, when an initial cycle is performed according to characteristics of the lithium secondary battery, a formation process for activating a cathode active material has to be essentially preceded. In the formation process, a large amount of gas may be generated in a battery cell. Thereafter, the generated gas may be removed through an opened or cut discharge hole. Then, the gas discharge hole may be thermally bonded and sealed. A process in which the gas within the battery cell is discharged, and then the discharge hole is thermally bonded as described above may be commonly called a degassing process. However, in the degassing process according to the related art, an electrolyte stained on a mechanism may be scattered due to the vacuum exhaust to contaminate a product.
Thus, a technology for solving the above-described limitations is needed.